Radar and Electronic Navigation

375 Pages·1988·9.838 MB·English

by  G. J. Sonnenberg (Auth.)

Radar and
Electronic Navigation
G. J. SONNENBERG, FRIN
Butterworths
London Boston Singapore Sydney Toronto Wellington
All rights reserved. No part of this publication may be reproduced or transmitted
in any form or by any means, including photocopying and recording, without
the written permission of the copyright holder, application for which should be
addressed to the Publishers. Such written permission must also be obtained before
any part of this publication is stored in a retrieval system of any nature.
This book is sold subject to the Standard Conditions of Sale of Net Books and
may not be re-sold in the UK below the net price given by the Publishers in their
current price list.
First published by George Newnes Ltd 1951
Second edition 1955
Third edition 1963
Fourth edition published by Butterworths 1970
Fifth edition 1978
Reprinted 1979,1980,1982
Sixth edition 1988
© Butterworth & Co. (Publishers) Ltd, 1988
British Library Cataloguing in Publication Data
Sonnenberg, G. J.
Radar and electronic navigation.—6th ed.
1. Electronics in navigation
I. Title
623.89'3 VK560
ISBN 0-408-01191-2
Library of Congress Cataloging-in-Publication Data
Sonnenberg, G. J. (Gerrit Jacobus), 1903-
Radar and electronic navigation.
Includes index.
1. Electronics in navigation. I. Title.
VK560.S6 1987 623.89'3 87-14699
ISBN 0-408-01191-2
Phototypesetting by En to En, Tunbridge Wells, Kent
Printed and bound in England at the University Press, Cambridge
Foreword
According to the Casualty Return of Lloyd's 1985 Register of Shipping the
number of 473 ships lost in 1978 was reduced to 307 in 1985, in spite of the
increase in the number of ships from 60 000 in 1978 to 75 000 in 1985.
Moreover, the 1985 ship losses were the lowest for the preceding 11 years.
This reduction may be partially explained by the increased application of
modern navigation and other electronic equipment during the last decade.
The development of this equipment is still continuing. The Global Posi-
tioning System, which is now under development, is capable of an accuracy
that was considered impossible two decades ago. The capability of radar sys-
tems to warn of collision threats by means of visual and audible alarms, and
to display courses by which collisions may be avoided, has also been greatly
improved.
To obtain the greatest benefit from the new, and often expensive, naviga-
tion systems, the basic principles and operation procedures of the various
systems must be studied, as well as the effects of the ionosphere and other
physical phenomena on their performance.
This sixth edition of Radar and Electronic Navigation explains these sub-
jects clearly without the use of complex mathematics. For this reason it is
recommended for use by marine academies and should be included in the
standing inventory of all merchant ships.
I wish the author and the book all the success they deserve.
J.N.F. Lameijer
Director, Royal Dutch Shipowners Association
Preface
Since publication of the fifth British edition, and the Russian and Taiwanese
editions, there has again been rapid development in navigational equipment,
necessitating numerous additions, omissions and improvements in this sixth
edition.
The Consol and Omega systems are now scarcely used on ships of the
merchant marine, so their descriptions are drastically reduced; because they
are based on the same principle as the Decca system, they have been
included in Chapter 4. The short chapter on integrated navigation systems
has been dropped, but there is a new chapter on the Global Positioning
System, which is planned to become operational in 1992. By the use of very
advanced electronic methods this satellite system will provide an accuracy
superior to that of all existing positioning systems.
In the first chapter and in the chapter on radar there are various additional
explanations of the side lobes of a radar main beam, some examples of Par-
allel Index Navigation, and the principles and use of Automatic Radar
Plotting Aids (ARPA). The Transit system is in widespread use and
although, according to current plans, it will become obsolete some two years
after the start of the GPS, it is still described.
Various subjects are now covered in more detail in an Appendix. Know-
ledge of these subjects is not essential to an understanding of the main part of
the book, however.
For the updating of the material on the Decca system I am much indebted
to Mr Claud Powell of Racal Decca, for the chapter on radar, to Mr G. Spies
of Radio-Holland, for the examples of Parallel Index Navigation, to Mr F. ten
Hoeve of the Nautical school in Rotterdam, and for the chapter on Transit to
Mr P. G. Sluiter, Geodetic and Hydrographie Consultant, and Mr A.
Wepster. The new chapter on the Global Positioning System could not have
been written without the very valuable help of Mr Sluiter.
This sixth edition was not, like the previous editions, translated from
Dutch but was written directly in English, and I would like to thank Mr Ken
Gorman for correcting faults in the language. Thanks also to Mr W.C.M. de
Ruyter for preparation of new illustrations, and last but not least to the staff
of Butterworths.
The following organizations and companies contributed to the book by
providing technical information and/or photographs:
Defense Mapping Agency, Hydrographie/Topographie Center, Washington
DC;
Directoraat-Generaal, Scheepvaart en Maritieme Zaken and Scheepvaart
Inspectie, Netherlands;
The Hydrographer of the Navy, Taunton, Somerset, UK;
The International Chamber of Shipping, London;
The Internationale Navigatie Apparaten BV, Rotterdam;
Krupp GmbH, Bremen;
Magnavox, Torrance, California, USA;
Marconi Marine, Chelmsford, UK;
Maritime Institute of Navigation, Rotterdam;
Philips, Netherlands;
Plath GmbH, Hamburg;
Racal Marine Electronics Ltd, UK;
The Royal Institute of Navigation, London, and its Netherlands Branch,
Amsterdam;
Sailtron, Utrecht, Netherlands.
G. J. Sonnenberg
Chapter 1
Introduction to marine navigation
The growth of electronic navigation systems during the last decades has been
dramatic. These aids to navigation, which have already proved of inestimable
value, are still advancing in scope and reliability.
Radar, developed primarily as an instrument for detecting and ranging in
warfare, is the most important electronic aid to navigation. Basically, radar
employs very short electromagnetic waves and utilizes the principles that
these waves can be beamed, that they travel at a constant speed in a straight
line, and that they will be reflected by anything they may meet. The reflec-
tions or echoes received provide information which is presented visually on
the screen of a cathode-ray tube.
Decca and Loran systems use radio signals transmitted by stations of
known position. Special receiving equipment enables the navigator to mea-
sure the difference between the arrival times of signals from two stations, and
thus to determine his position. The most accurate system for position fixing is
the Global Positioning Satellite system (GPS) which will have world-wide
coverage. Underwater navigational aids include the echo depth sounder and
the Doppler log.
This chapter covers the fundamental theory which must be understood
before these systems and their applications can be described in detail. Three
of the systems (radar, the direction finder and the echo sounder) make use of
the cathode-ray tube, so an outline of the principles of its operation is
included. Consol, Loran and Decca are hyperbolic navigation systems, that
is, the lines of position provided by them have a hyperbolic character. There-
fore the properties of hyperbolas are discussed. As satellite position fixing
and the Doppler log are based on measurements of the Doppler shift, this
phenomenon will be described too. The manner in which radio waves are
generated, propagated and reflected by the ionosphere and by the Earth's
surface is also covered. These reflections have a great influence on the range
over which the various position-fixing systems can be received and on the
accuracy of the position fix obtained. First of all, however, alternating cur-
rents and voltages, phase differences, radiation and receivers will be dis-
cussed.
Alternating currents and voltages
A complete series of alterations occuring so that the conditions at the end are
identical with those at the beginning constitutes a cycle. A graph of an alter-
1
2 Introduction to marine navigation
nating current is shown by a plot of the current, /, versus time, t (Figure 1.1).
The current at ^ is the same as at t ; therefore one cycle has elapsed between
0
t and ^. 7 is the maximum value of the current or the amplitude. An altern-
0 max
ating voltage can be described by a similar curve. For some purposes an
angle, a, is indicated instead of the time on the horizontal axis. In that case
each cycle starts at ^ when a = 0° and at the end of the cycle a = 360°.
Time, t
Figure 1.1 Curve of an alternating current (sine wave)
The instantaneous value of a normal current /= 7 sin a; hence, the plot
max
of current versus time is a sine wave. Alternating currents and voltages may
have shapes other than sine or cosine curves, however.
The number of cycles per second is the frequency and this is a very
important parameter throughout this book. The electricity supply in most
countries is an alternating voltage with a frequency of 50 cycles per second
or 50 hertz (Hz). In radio techniques, the audio or low frequencies (between
about 100 Hz and 18 000 Hz) are an important frequency range. These fre-
quencies, when supplied to a loudspeaker, produce audible sound waves of
the same frequency in the air. Other important frequencies are the radio or
high frequencies which are higher than about 10 000 Hz. Frequencies
between 10 000 and 18 000 Hz are either radio or audio frequencies,
depending upon their origin and applications.
One thousand hertz is conveniently written as one kilohertz (1 kHz), and
one million hertz as one megahertz (1 MHz). In radar, frequencies of
10 000 MHz are common. To avoid the use of large numbers, the unit giga-
hertz (GHz; 1 GHz = 1000 MHz) is often used; 10 000 MHz = 10 GHz.
Phase differences
Two alternating currents or voltages of the same frequency are in phase
when they reach their positive maximum value at the same time. Figure 1.2
shows two equal alternating currents; the current ^ lags behind i by a
x
quarter of a cycle, or by 90°. If the phase difference is 180°, the maximum
positive swing of i will coincide with the maximum negative swing of 4-
x
Two alternating currents or voltages can differ in frequency, amplitude
and phase. Figure 1.3(a) shows two alternating voltages of the same fre-
quency but of differing phase and amplitude. The voltage e leads e by 45°
x 2
and has a greater amplitude, 40 V compared with 30 V for e .
2
Like forces and velocities, sine-wave voltages and currents may be indi-
cated by vectors. The length of the vector representing a force is propor-
tional to the magnitude of the force, and the direction of the vector indicates
Introduction to marine navigation 3
Figure 1.2 Two alternating currents with equal amplitudes and frequencies but a phase
difference of 90°
£i = 40 V
E =30V
Time, t 2
(b)
Figure 1.3 (a) Alternating voltage e (maximum value 40 V) leads e (maximum value 30 V) by
x 2
45°; (b) vector diagram of the two voltages
the direction of the force. The length of a vector representing an alternating
voltage is proportional to the amplitude.
In Figure 1.3(b) the two voltages shown in Figure 1.3(a) have been plotted
as vectors. Their phase difference is 45°. One of the vectors, for instance, E ,
2
may be given any direction; but Ε must then be plotted in a direction
λ
leading E by 45°. If the instantaneous voltage e = E sin ω t, then
2 2 2
e = E sin (ω t+ φ), where φ is the phase difference between e and e , in this
1 l x 2
case 45°, and ω = 2 it f.
If there are two sine-wave currents or voltages of equal frequency in the
same circuit, the resulting current or voltage can be found as shown in Figure
1.4(a). The vectors I and I indicate two alternating currents. Their resultant
2 2
is the diagonal I of the parallellogram. Conversely, an alternating current or
r
voltage can be resolved into two or more components. In Figure 1.4(b) I is
r
resolved into, for instance, I and I , and I into I and I . Hence I is the
c ab ab a b r
resultant of I , I and I .
a b c
4 Introduction to marine navigation
Figure 1.4(a) Ir is the resultant of Ix and I2; because Ix and
I2 are sine waves, IT is also a sine wave
Figure 1.4(b) IT is the resultant of /a, 7b and Ic; conversely, IT can
be resolved into Ia, Ih and Ic
Due to the ease with which the resultant of two or more alternating cur-
rents and voltages can be determined, and the clarity with which phase differ-
ences and the magnitude of the currents and voltages may be shown, vector
diagrams, rather than curves (as Figure 1.3(a)), are generally used in radio
techniques and electronics.
Electromagnetic radiation
According to the laws of electricity, a current passing through a wire pro-
duces a magnetic field around the wire. The number of magnetic lines of
force (the strength of the field) is proportional to the current (Figure 1.5).
Looking in the direction of the current, the circular magnetic lines of force
have a clockwise direction. If the current continually changes its magnitude,
and periodically changes its direction, the magnetic field does the same. This
field is called the induction field.
Thus far, only audio frequencies have been considered. As proved by
Maxwell in 1888, a radio frequency current generates a radiation field simul-
taneously with the induction field. The radiation field consists of magnetic
lines of force of the same circular shape as those of the induction field. If the
current decreases and ultimately disappears, the magnetic lines of force of
the induction field shrink correspondingly, i.e., the radii of their circles
decrease to zero. The radii of the lines of force of the radiation field, how-
ever, continue to increase, independent of the current in the antenna. In
Introduction to marine navigation 5
S V
- > ; );
Figure 1.5 Induction field; magnetic lines of force produced by
an electric current. When the current increases or decreases,
the radii of the circles also increase or decrease
other words, once generated, there is no longer any relation between the con-
tinuously expanding radiation field and the current in the antenna.
Figure 1.6 shows a radio frequency current supplied to the vertical wire of
an aerial at the centre O. Due to the rapid and continually repeating increase,
deci ease and reversal of direction of the current in the wire, a radiation field
arises. The lines of force shown with an arrow in the clockwise direction,
were caused by a current that was directed away from the observer, and
those with an opposite arrow, by an opposite current. The lines of force
between A and B, for example, were generated by one cycle of the alternating
current. This distance is called the wavelength. The lines of force travel
300 000 km/s. This propagation velocity basically remains the same, irre-
spective of the frequency or of the current in the wire. If the frequency and/or
the current increases, the density of the magnetic field and hence, the radi-
ated power, will also increase. However the velocity of propagation does not
increase.
If the frequency is/Hz, there are/cycles per second, and thus/waves per
second are generated. These/waves travel a distance of 300 000 km in one
second, so the length λ (lambda) of one wave is:
300 000 300 000 000
λ = km = m
/ /
Using this formula, the wavelength can be calculated if the frequency is
known, and vice versa. Normally the radiation field is indicated by its fre-
quency, rather than by its wavelength. One wavelength (for example AB in
Figure 1.6) is also the distance covered by a line of force or a wave during one
cycle.
If the velocity of propagation is indicated by c, the formula λ = c/f is also
applicable to sound waves in air and water. In air, eis about 330 m/s and in
water eis about 1500 m/s.